This device applies more particularly to electronic data processing units integrated with semiconductors, including volatile components for the storage of data or programs, or for the processing of signals or information, for example such as credit cards having integrated microprocessors. These units may also be made up at least partly by digital counters, or may include quartz clocks.
Electronic data processing units that include volatile memories (such as RAM) have the disadvantage that they lose all the information contained in these memories in the absence of a source of electrical power. This is true for instance for credit cards of the electronic type, which include an integrated microprocessor associated in particular with such memories.
The same disadvantage is found in more conventional electronic units, such as the aforementioned counters, which except for the digital display apparatus are in the form of integrated circuits having multivibrators as their primary components. When these components are connected to voltage, their initial state is always the same, because a reset to zero takes place whenever such counters are reconnected to voltage.
In an integrated electronic unit such as a credit card having a microprocessor and a volatile memory, it may be necessary for reasons of security, especially when the cell or battery that supplies the unit is contained within the card, to prevent any resumption of function of the card when the cell or battery that supplies the integrated electronic unit contained in this card has been taken out (thus causing a cutoff of electrical power) and then put back so as to reconnect the electronic unit to voltage. When this card is used for instance to withdraw money from a cash distributing bank terminal, the card holder must first make his personal access code known, so that the withdrawal can be authorized by the processing system that is connected to the terminal. Typically, the card includes an integrated counter that memorizes the number of attempts made by the card holder to indicate his personal access code to the terminal. The number of attempts at introducing the access code is limited in a predetermined manner, such that after a predetermined number of unsuccessful attempts, the card is retained by the terminal, since the counter has reached the predetermined number that is not to be exceeded. The holder, now having lost his card, must consult with the bank to recover it.
In the case where the card holder is a defrauder, who since he does not know the exact access code would like to make a great number of successive attempts to discover the access code without allowing the counter to play its role in security, it would be possible for him to remove or disconnect the battery or power cell of the electronic data processing unit of the card, so that the cutoff of power would automatically reset the counter to zero. Once this reset to zero has been done, the defrauder need merely replace the cell to resupply power to the electronic unit of the card and to gain access successfully each time to the internal memories, since the access code will have been reset to the initial known state; the cell can be removed again before the predetermined number of attempts that is not to be exceeded, and which is recorded by the counter, has been reached, and so on.
It is clearly important in this case to provide a security device that prohibits the execution of one or more functions, or even the entire functioning of the electronic data processing unit carried by the card, after any initial cutoff of the power supply to this electronic unit.
Another example where the role of such a security device can be important is that of an integrated electric counter that records the distances traveled by a vehicle. If the power supply to this counter is autonomous and integrated with the counter, a defrauder might be tempted to cut the power to reset the counter to zero. The resumption of voltage to the counter would then enable the defrauder to begin again, much more advantageously, in terms of the evidence of the distance traveled, especially when he wants to sell his vehicle.
Another example of an electronic data processing unit for which a security device that prohibits its functioning is desirable is one in which the electronic unit includes a quartz clock, the functioning of which is no longer assured as soon as the internal electric power source becomes defective. In this case, the time base fixed by the quartz clock goes awry without the knowledge of the user of the electronic unit, and this may have very important consequences if the electronic unit is for instance one that furnishes standard measures. In that case, it is useful to prohibit the function of the unit if the clock power supply has been cut off and then resumed, so that the user will be informed of the cutoff and will recalibrate the unit.
At the present time, no reliable security devices having a simple structure and low cost, and which enable prohibiting the function of one or more functions of an electronic data processing unit, or even the function of the unit, after a first cutoff of its power supply and a subsequent resumption of voltage to the unit, are known.